It has been known that a polysilazane, particularly a perhydropolysilazane soluble in an organic solvent is useful as a silicon nitride precursor (see Patent document 1, for example). In recent years, it has been known that a method in which a coating composition comprising a polysilazane is applied and then converted into a siliceous film by curing, as a method for forming an interlayer dielectric in electronic devices such as a semiconductor device (see Patent documents 2 to 5, for example).
The perhydropolysilazane has a repeating unit represented by —SiH2—NH— and Patent document 1 discloses a synthesis method of perhydropolysilazane, in which adducts composed of a dihalosilane and a base are reacted with ammonia.
In addition to this, there have been proposed various other methods for synthesizing a polysilazane, such as (a) a method for reacting a silicon halide such as SiCl4, SiH2Cl2 or the like with an amine, (b) a method for preparing a polysilazane from a silazane by use of a dehydrogenating catalyst consisting of an alkali metal hydride such as KH, (c) a method for synthesizing a silazane by a dehydrogenation reaction of a silane compound and an amine compound by use of a transition metal complex catalyst, (d) a method for preparing a polysilazane by performing an amine exchange of aminosilane with ammonia by use of an acid catalyst such as CF4SO3H, (e) a method for performing an amine exchange of an aminosilane with a large amount of ammonia or amine, (f) a method for performing an amine exchange reaction of a polyvalent aminosilane compound with a polyhydrogenated nitrogen-containing compound in the presence of a basic catalyst, etc. (see Patent document 6, for example).
The film formed by converting the polysilazane into siliceous materials is used as various kinds of films such as a passivation film, a protective film, and a planarization film in electronic devices such as a semiconductor device other than the aforementioned interlayer dielectric. However, these films in the electronic devices require various properties such as an insulation property, flatness of a film, resistance to an acid, an alkali, solvent, and the like, a high barrier property, and so on. Though a film fulfilling these properties can be produced by forming a siliceous film by use of a coating liquid containing the polysilazane, siliceous films having high withstand voltage characteristics and an excellent solvent resistance property cannot be obtained by a low temperature curing when the perhydropolysilazane is used as the polysilazane. Therefore, for converting the perhydropolysilazane into a siliceous film having an excellent insulation property, high withstand voltage characteristics, and an excellent solvent resistance property, it was necessary to contact the siliceous film with steam at a high temperature.